JP2005099195A - Optical transmission body and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress distortion, cracks and bubbles caused on clad inner surface when a core is generated in a clad. <P>SOLUTION: A core 30 is generated by injecting core monomer with dopant into a clad 12 and polymerizing them. Then, the temperature of the core monomer is adjusted so that the following relationships, i.e., Tg-60≤TC≤Tb or 40≤TC≤Tb are satisfied where TC(°C) is the temperature of the core monomer when it is injected, Tg(°C) is the temperature of the glass transition point of the polymer made of the clad 12 and Tb is the boiling point of the core monomer in ordinary pressure. The clad 12 is processed under the reduced pressure. Polymerization of the core monomer is conducted by a polymerization device in nitrogen atmosphere while it is pressurized and heated. In the preform obtained by the above processes, no distortion, cracks and bubbles are caused on the clad inner surface and the optical fiber obtained from the preform has a good optical characteristic. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

    The present invention relates to an optical transmission body and a manufacturing method thereof, and more particularly to an optical transmission body that can be used for a plastic optical fiber, an optical waveguide, and the like, and a manufacturing method thereof.

  In optical applications such as optical transmitters, plastic materials are generally superior to quartz materials in terms of molding processability, weight reduction, cost reduction, flexibility, and impact resistance. doing. For example, a plastic optical fiber (POF) is not suitable for long-distance optical transmission because of a large optical transmission loss compared to a quartz optical fiber. The diameter can be increased to several tens of μm or more. This increase in the diameter eliminates the need to increase the connection accuracy of various peripheral parts and devices used for branching and connection of the optical fiber with the optical fiber. Therefore, the plastic optical fiber has the merit that connection with peripheral parts and devices, ease of terminal processing, and high-precision alignment are unnecessary. In addition to the cost reduction of the connector part as described above, the plastic optical fiber has a low risk of puncture accidents on the human body due to the properties of the plastic, easy processability due to high flexibility, There are advantages such as easy installation, vibration resistance, and low price. As a result, plastic optical fibers are not only attracting attention for home and in-vehicle applications, but also as ultrashort-distance and large-capacity cables such as internal wiring of high-speed data processing devices and DVI (digital video interface) links. , Use is being considered.

  The plastic optical fiber includes a core portion and a clad portion, and is also called a plastic optical fiber strand. Generally, the core part is a core part made of an organic compound having a polymer as a matrix, and the clad part is an outer shell part having a refractive index lower than that of the core part.

  The plastic optical fiber can be produced by drawing a polymer and simultaneously molding the core or clad into a fiber, or by manufacturing an optical fiber preform (hereinafter referred to as a preform) and then melting the preform. There are methods such as stretching.

  A refractive index distribution type plastic optical fiber has recently attracted attention as an optical fiber having a high transmission capacity, which is a plastic optical fiber including a core portion having a refractive index distribution from the center toward the outside. One of the methods for producing the gradient index POF utilizes an interfacial gel polymerization method. In this method, a preform is first prepared as described above, and then the preform is melt-drawn. In this production method, first, a polymerizable compound such as methyl methacrylate (MMA) is placed in a sufficiently rigid polymerization vessel, and the polymerizable compound is polymerized under predetermined conditions while rotating the polymerization vessel (hereinafter, referred to as “polymerization compound”). A cylindrical tube made of a polymer such as polymethylmethacrylate (PMMA) is produced by a method called rotational polymerization. This cylindrical tube becomes a clad portion. Next, the raw material of the core portion is injected into the hollow portion of the cylindrical tube, and interfacial gel polymerization is performed inside the cylindrical tube to form the core portion. Examples of the raw material for the core include a polymerizable compound such as MMA, an initiator, a chain transfer agent, and a refractive index adjuster. The core portion formed by the interfacial gel polymerization has a concentration distribution of the refractive index adjusting agent and the like contained therein, thereby causing a refractive index distribution in the core portion. The preform thus obtained is heated and stretched in an atmosphere of about 180 ° C. to 250 ° C. to obtain a gradient index plastic optical fiber. (For example, see Patent Document 1)

  The plastic optical fiber manufactured in this way is rarely used as it is, and in many applications, a protective coating is applied to the outer periphery (for example, formation of a protective layer) or in a tube having a predetermined inner diameter. Inserted and used. By protecting the outer periphery in this way, scratches, damage, structural irregularities such as microbending, and deterioration of optical properties are observed during handling of plastic optical fibers and when plastic optical fibers are used in adverse environments. Plastic optical fiber can be protected.

Japanese Patent Laid-Open No. 11-337781 (page 6, FIG. 2)

  However, for example, in the case of manufacturing a plastic optical fiber through a preform, a polymerizable compound for generating a core portion is injected into the previously formed cladding portion in the preform manufacturing process. In this case, cracks or the like may occur on the inner surface of the clad part, or bubbles may be generated at or around the boundary with the core. Many cracks occur particularly when the inner surface of the clad portion is distorted in advance. In addition, bubbles are generated due to volume reduction due to polymerization shrinkage and vaporization of dissolved by-products and dissolved low-boiling substances during core formation.

  The crack affects the refractive index when it is a plastic optical fiber and causes a decrease in transmission performance, and the bubbles remain even when the plastic optical fiber is melted and stretched. Like cracks, it causes light scattering and reduces the transmission performance and productivity of plastic optical fibers. In addition, if there are bubbles, the bubbles expand in volume due to heating during melt drawing and cause cracks. The generation of such cracks and bubbles is a problem that may also occur when manufacturing an optical transmission body other than a plastic optical fiber, such as an optical waveguide or a lens. That is, even if it is another optical transmission body, the 2nd member adjacent to the 1st member is generated by giving a polymerization compound to the surface of the 1st member like the above-mentioned clad, and polymerizing this. This often occurs when using such a manufacturing method.

  Therefore, the present invention provides an optical transmission body that gives a polymerizable compound to a first member formed in advance and polymerizes the first compound, thereby producing a second member adjacent to the first member. An object of the present invention is to provide an optical transmission body that suppresses cracks and bubbles generated in the method and has good optical characteristics, and a method for manufacturing the same.

  In order to solve the above problems, in the present invention, an injection step of injecting a polymerizable compound into a first member formed into a tubular shape from a material containing a polymer, and a second member by polymerizing the polymerizable compound In the method for producing an optical transmission body using the polymerization step, the temperature of the polymerizable compound in the injection step is TC (° C.), and the glass transition point of the polymer of the first member is Tg (° C. And when the boiling point of the polymerizable compound is Tb, Tg−60 ≦ TC ≦ Tb or 40 ≦ TC ≦ Tb is satisfied.

  Prior to the injection step, it is preferable that at least the inner surface of the first member is kept under reduced pressure for a predetermined time. The polymerizable compound is more preferably polymerized under heating. This polymerizable compound is preferably polymerized under pressure.

  The first member preferably has at least one layer formed by a rotational polymerization method or a layer formed by a melt extrusion method. This is the case where the first member is a single layer or multiple layers, and in the case of a single layer, the layer is formed by a rotational polymerization method, and is molded by a melt extrusion method. In the case of a multi-layer, it includes a case where both a layer formed by a rotational polymerization method and a layer formed by a melt extrusion method are included.

  The second member preferably has a higher refractive index than the first member, and the composition containing the polymerizable compound produces a polymer having a higher refractive index than the first member, and the composition Is more preferably included in the second member. The refractive index of the first member or the second member decreases continuously or stepwise from the center in the radial direction of the cross-sectional circle toward the outer periphery, and the difference between the maximum value and the minimum value of the refractive index is More preferably, it is 0.001 or more and 0.3 or less. Moreover, it is preferable that a 1st member contains a fluorine-containing polymer. Note that at least the inner surface of the first member preferably contains an amorphous polymer.

  Then, the optical transmission body obtained by the above manufacturing method is melt-drawn to obtain an optical fiber, at least a part of the first member is a clad portion of the optical fiber, and the second member is a core portion of the optical fiber. It is preferable to become.

  Further, the present invention includes an optical transmission body manufactured by the above manufacturing method and an optical fiber.

  In the method of manufacturing an optical transmission body of the present invention, a light that generates a second member adjacent to the first member by applying a polymerizable compound to the first member formed in advance and polymerizing the polymerizable compound. Cracks and bubbles generated in the method for manufacturing the transmission body can be suppressed. And the optical transmission body of this invention expresses a favorable optical characteristic.

  Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In this embodiment, a plastic optical fiber (hereinafter referred to as POF) is illustrated, but the present invention is not limited to POF, and can be applied to various optical transmission bodies. Other optical transmission bodies include optical waveguides, etc., and here, planar lenses, spherical lenses, aspheric lenses, fiber lasers, fiber amplifiers, filters, etc. are also exemplified, and these are combined and configured. Also included. Examples of combinations include a combination of an optical fiber, a lens, a fiber laser, and a fiber amplifier.

  FIG. 1 is a manufacturing process diagram of a POF and an optical fiber cable. Each process will be described in detail later, and only the flow of the process will be described here. First, a tube-shaped clad 12 is created by the clad creating step 11. The clad 12 is a portion that forms an outer shell portion of a preform to be produced later. Thereafter, a core polymerization process is performed in order to generate a core inside the clad 12. The preform 15 is obtained by generating the core. The preform 15 is stretched by the stretching process 16 to become a POF 17. In the stretching step 16, the columnar preform 15 is heated and stretched in the longitudinal direction. Even if the preform 15 is not the POF 17, it remains in this state and functions as an optical transmission body. Then, the POF 17 becomes a plastic optical fiber cable 22 through a covering step 21 in which the outer periphery is covered with a covering material.

  Next, the POF and the manufacturing method thereof according to the present embodiment will be described with reference to FIGS. FIG. 2 is a cross-sectional view of the preform, and FIG. 3 is a diagram showing the refractive index in the radial direction of the cross section of the preform. FIG. 4 is a cross-sectional view of a polymerization apparatus for generating a core in the cladding.

  A preform 15 shown in FIG. 2 includes a clad 12 that is an outer shell portion and a core 30 in the clad 12. When the clad 12 and the core 30 are made POF by stretching, they become the core and clad of the POF, respectively. The clad 12 has a tubular shape with a constant outer diameter and inner diameter in the longitudinal direction and a uniform thickness, and one end is blocked. In this embodiment, the clad 12 is made of polymethyl methacrylate (hereinafter referred to as PMMA), and is manufactured by a rotational polymerization method. The clad 12 is thus made of a polymer obtained by polymerizing a polymerizable compound. In the following description, the polymerizable compound for forming the clad 12 is referred to as a clad monomer, and a polymer formed by polymerizing the clad monomer is referred to as a clad forming polymer. The production of the clad 12 in this embodiment may be performed by a rotational polymerization method in which the clad 12 is formed into a tubular shape while performing its polymerization reaction, as in the case of producing PMMA from MMA, or a polymer is obtained from other clad monomers. In some cases, the polymer is formed into a tubular shape by melt extrusion molding. However, in the description of the present embodiment, the case where the clad monomer is MMA and the clad forming polymer is PMMA is taken as an example. Details of the clad material and manufacturing method will be described later.

In FIG. 3, the horizontal axis indicates the cross-sectional radial direction of the preform, and the vertical axis indicates the refractive index. The refractive index means that the upper direction has a high value. The range indicated by the symbol (A) on the horizontal axis is the refractive index of the cladding 12 in FIG. 2, and the range indicated by the symbol (B) is the refractive index of the core 30 in FIG. As shown in FIG. 3, the core 30 has a refractive index that continuously increases from the boundary with the cladding 12 toward the center. The refractive index of the cladding 12 is lower than the refractive index of the core 30.
In the radial direction of the circular cross section, the difference between the maximum value and the minimum value of the refractive index is preferably 0.001 or more and 0.3 or less. With this structure, the preform 15 exhibits a function as an optical transmission body, and an optical fiber is obtained by stretching the preform 15. Thus, the POF made by stretching the preform 15 whose refractive index continuously changes from the cladding 12 of the outer shell portion toward the center in the longitudinal direction is called a graded index (GI) POF. . And in the present invention, as shown in FIG. 3, the refractive index of the core 30 of the manufactured preform 15 is such that the refractive index continuously increases from the outside of the circular cross section toward the center. As a method for generating the core 30, an interfacial gel polymerization method as described below is applied.

  First, a polymerizable compound that is a raw material for generating the core 30 is injected into the clad 12. In the following description, the polymerizable compound for generating the core 30 is referred to as a core monomer. In this embodiment, the core monomer is methyl methacrylate (hereinafter referred to as MMA). However, the core monomer is not limited to MMA, and other monomers may be used. Examples of suitable core monomers other than MMA will be described later together with the material of the cladding 12.

  In the present invention, the temperature of the core monomer is adjusted prior to the above injection. Specifically, the glass transition point of the clad forming polymer, that is, PMMA in this embodiment, is Tg (° C.), the boiling point of the core monomer is Tb (° C.), and the temperature at which the core monomer is injected into the clad 12 Is set to TC (° C.), the temperature of the core monomer is adjusted so as to satisfy Tg-60 ≦ TC ≦ Tb. More preferably, Tg-50 ≦ TC ≦ Tb, and most preferably Tg-30 ≦ TC ≦ Tb. In addition, when these lower limits are less than 40 degreeC, it heats to 40 degreeC or more which is a temperature higher than room temperature. The upper limit is more preferably Tb-10 (° C.) in terms of control. By satisfying this condition, when the core monomer is filled in the clad 12, the temperature of the clad 12 rises from the inner surface, and the higher the temperature, the higher the molecular energy of the clad-forming polymer. The affinity of the core monomer with the molecule is improved. In the swelling layer in the initial stage of polymerization of the core monomer, which will be described later, the molecular density is uniform and the orientation of the inner surface of the cladding 12 and the molecules in the vicinity thereof are made uniform. Cracks and the like can be suppressed.

  The energy of the molecules of the clad forming polymer increases as the temperature is lower than the glass transition point Tg and becomes closer to Tg, and further increases in the temperature region exceeding the glass transition point Tg. Therefore, the temperature TC of the core monomer at the time of injection may be higher than the glass transition point Tg of the clad forming polymer. However, the upper limit of TC must be in a range that does not deteriorate the good optical characteristics and mechanical strength of the preform 15 to be obtained as an optical transmission body. For example, even if TC is set to a temperature higher than the glass transition point Tg of the clad-forming polymer and the clad-forming polymer is cooled after its Tg is exceeded and the alignment state is changed from the molecules before the Tg, The refractive index, elastic modulus, etc. must be within a predetermined range.

  The boiling point Tb of the core monomer means the boiling point at normal pressure in this embodiment. This is because in this embodiment, the core monomer is injected into the cladding 12 under normal pressure. When the core monomer needs to be injected under reduced pressure, the boiling point Tb of the core monomer is set as the boiling point Tb of the core monomer, and the temperature TC at the time of injection of the core monomer is adjusted to the above range. .

  The temperature adjustment of the core monomer is preferably performed within a range in which the core monomer does not decompose, vaporize, polymerize, or the like. For example, if the core monomer does not change in quality, the temperature may be adjusted in a state where a dopant or the like is added. In order to stabilize the core monomer, the temperature may be adjusted in an inert gas atmosphere such as nitrogen or argon as necessary, or the dissolved gas is replaced with an inert gas or after replacement. In some cases, it is preferable to adjust the temperature. This temperature adjustment method is appropriately determined according to the type of the core monomer used. In the present embodiment, although not shown in the drawings, a method is used in which the core monomer is placed in a container or the like and placed in a thermostatic bath for a predetermined time. However, the present invention is not limited to this method. For example, there is a method of adding a monomer for use and adjusting the heat transfer medium in the jacket to a predetermined temperature.

  In the present invention, it is more preferable that the clad 12 before being filled with the core monomer is kept under reduced pressure for a predetermined time. By this decompression treatment, water or air contained in the clad forming polymer is heated during the polymerization of the core monomer and the like, and the volume of the clad 12 is expanded. Or a phenomenon in which the molecular density inside the preform 15 varies.

  Further, when MMA, which is a core monomer, is injected into the clad 12, a polymerization initiator, a chain transfer agent, and an appropriate refractive index adjuster (dopant) are injected together with the core monomer. Each addition amount of these polymerization initiators, chain transfer agents, and dopants will be described later. Note that the refractive index in the radial direction of the cross section of the core 30 can also be changed by using, for example, two or more kinds of core monomers without using a dopant. In the present embodiment, a low molecular compound having a high refractive index and a large molecular volume and not participating in polymerization is used as a dopant, and the refractive index in the radial direction of the core 30 is changed by adding this.

  Polymerization of the core monomer is performed by a polymerization apparatus 40 as shown in FIG. The polymerization apparatus 40 includes a thermometer 47 and a temperature controller 48 in addition to a polymerization vessel 41, a pressure gauge 44, and a pressure controller 45. Further, the polymerization container 41 is provided with a nitrogen supply source 51 for supplying nitrogen as an inert gas. The polymerization container 41 has a container main body 41a and a lid 41b, and the container main body 41a and the lid 41b are fixed by screws (not shown). However, the present invention does not depend on the structure of the polymerization apparatus, and a different apparatus from the polymerization apparatus 40 shown in FIG. 2 may be used.

  The pressure gauge 44 detects the pressure inside the polymerization vessel 41. The pressure controller 45 controls the pressure inside the polymerization vessel 41 by adjusting the amount of nitrogen supplied from the nitrogen supply source 51 according to the detection result of the pressure gauge 44. The thermometer 47 detects the temperature inside the polymerization vessel 41. The container body 41 a is provided with a heating wire (not shown), and the temperature controller 48 controls the current flowing through the heating wire according to the detection result of the thermometer 47. Thereby, the temperature inside the polymerization vessel 41 is controlled. The supplied gas is not limited to nitrogen as long as it is an inert gas, and may be argon or the like. By this gas supply, the internal air of the polymerization vessel 41 is replaced with nitrogen. The polymerization container 41 is capable of finely controlling the internal pressure and the supply amount of nitrogen to the inside by screwing the container main body 41a and the lid 41b.

  The clad 12 is inserted into a glass tube 52 as a jig in a state in which a mixture of a core monomer and a polymerization initiator, a chain transfer agent, a dopant, and the like is injected, and is placed in a container body 41a. At this time, the glass tube 52 is left still vertically. The clad 12 in which the core monomer or the like is injected is preferably subjected to deaeration before being inserted into the glass tube 52 or in the inserted state. As this degassing treatment method, in view of simplicity and effect, a decompression process using a decompression chamber or the like is preferable, and it is more preferable to apply an ultrasonic wave in the decompression process. The decompression process is more preferably performed for 30 minutes or more in a decompression chamber or the like.

  When the clad inserted glass tube 52 is set on the container body 41a and the lid 41b is screwed to the container body 41a, nitrogen is supplied from the nitrogen supply source 51 to the inside of the polymerization container 41, and the valve V1 is turned on. By opening the air, the air inside the polymerization vessel 41 is discharged, and the air inside the polymerization vessel 41 is replaced with nitrogen. After nitrogen substitution, the internal pressure of the polymerization vessel 41 is controlled by the pressure controller 45 so as to be a predetermined value. The polymerization of the core monomer is performed while being heated by the temperature controller 48. The polymerization is performed at a predetermined temperature for a predetermined time. The pressure during the polymerization reaction is controlled to be a predetermined value by the pressure controller 45 and is preferably higher than the normal pressure.

  When the core monomer starts polymerization, the inner wall of the clad 12 is swollen by the core monomer, and a swelling layer is formed at the initial stage of polymerization. This swelling layer is in a gel state, and therefore the polymerization rate is accelerated (referred to as gel effect). Then, the polymerization starts from the inner surface of the clad 12 and proceeds toward the center of the circular cross section of the clad 12. At this time, since a compound having a smaller molecular volume enters the swelling layer preferentially, a dopant having a large molecular volume is pushed out from the swelling layer toward the center as the polymerization proceeds. As a result, the preform with the refractive index gradually increased toward the center in the radial direction of the circular cross section as shown in FIG. Can be obtained. In the present embodiment, the clad 12 and the core 30 are both made of PMMA, and the preform 15 is created while forming the swelling layer as described above. It does not have a critical boundary. That is, FIG. 2 shows the boundary between the clad 12 and the core 30 for convenience of explanation, but in this way, the production conditions such as the material of the clad 12 and the core 30 and their affinity, or the presence or absence of the swollen layer formation, etc. Accordingly, the clarity of the boundary between the clad 12 and the core 30 in the obtained preform 15 is different.

  Further, at the time of polymerization of the core monomer, it is preferable that the clad 12 into which the core monomer is injected is supported by a jig such as a glass tube 52 and set in the polymerization vessel 41 as shown in FIG. It is particularly preferable that the jig has a tubular shape having a hollow part into which the clad 12 can be inserted. And as polymerization progresses under pressure, the force to gradually shrink the region that becomes the core 30 increases, but the jig can be dimensionally changed in a minute range accordingly. The clad 12 is preferably supported without fixing the outer surface of the clad 12. For example, when the clad 12 is fixed and supported by a jig, the clad 12 cannot respond to the shrinkage of the core 30 during polymerization, and voids are easily generated in the central portion of the core 30. turn into. For these reasons, when the jig is tubular, it is preferable to have an inner diameter larger than the outer diameter of the clad 32. The inner diameter of the tubular jig preferably has a diameter that is larger by 0.1% to 40% than the outer diameter of the cladding 12, and has a diameter that is larger by 10 to 20%. More preferred. However, the cladding 12 is preferably used as long as it can stand upright and supports the cladding 12 according to the dimensional change of the cladding, and does not need to be tubular.

  The preferred range of pressure during polymerization is appropriately determined depending on the core monomer used. If the degree of pressurization is too large, the pressurized gas dissolves in the core monomer, or the dissolved gas present in the core monomer does not desorb, and this becomes a bubble in the stretching step 16 (see FIG. 1) by heating. There is a problem. On the other hand, when the degree of pressurization is too small, there is a problem that the responsiveness is low with respect to the volume shrinkage at the time of polymer production in the polymerization process of the core monomer, and voids and bubbles are likely to be generated. In the present embodiment, about 0.01 MPa to 1.0 MPa was a preferable range. Thus, by controlling the pressure at the time of polymerization, it is possible to suppress the generation of voids and bubbles in the core 30 of the preform 15 or the core portion of the POF.

  The polymerization is preferably performed under heating as shown in the present embodiment. The temperature is determined according to the type of the monomer for the core and the like, and is determined mainly considering the polymerization rate and the modification temperature. For example, when a typical methacrylate-based low molecular weight compound is used as the core monomer and used as the main component of the core 30, the temperature is preferably 50 ° C to 150 ° C, and 80 ° C to 140 ° C. More preferably. The polymerization time is preferably 4 to 48 hours, but this is also determined according to the type of the core monomer. However, in the present invention, the conditions during polymerization are not limited to those described above.

  In this manner, a preform 15 that is a cylindrical optical transmission body in which the core 30 and the clad 12 are made of plastic can be manufactured, and the obtained preform 15 is subjected to a stretching process. Then, by stretching, a POF having a desired diameter, for example, 200 μm or more and 1000 μm or less can be obtained.

  The present invention is not limited to the case of manufacturing the preform 15 as shown in FIG. For example, the present invention is also applicable when the clad or core has a multilayer structure. As an example, another embodiment of the present invention will now be described with reference to FIGS.

  FIG. 5 is a schematic view showing a manufacturing process of POF as another embodiment. First, a pipe having a clad and an outer core is manufactured by the pipe making process 61. The clad is the outermost shell of the preform, similar to the clad 12 in FIG. The outer core is formed on the inner surface of the clad so that the center of the cross section of the preform is hollow. Next, the inner core polymerization step 63 is a step of generating an inner core in the outer core, that is, in the hollow portion, and the preform 65 is obtained through this inner core polymerization step. Therefore, the preform 65 here has an outer core and an inner core as cores. The preform 65 is stretched by the stretching process 66 to become POF 67. However, the preform 65 has a core and a clad and exhibits a function as an optical transmission body without going through the stretching process. In this stretching step, the cylindrical preform 65 is heated and stretched in the longitudinal direction. Then, the POF 67 becomes a plastic optical fiber cable 72 through a coating process 71 in which the outer periphery is coated with a coating material.

  FIG. 6 is a cross-sectional view of the preform, and FIG. 7 is a diagram showing the refractive index in the radial direction of the cross-section of the preform. In FIG. 7, the vertical axis and the horizontal axis are the same as those in FIG. A preform 65 shown in FIG. 6 includes a clad 75 which is an outer shell, an outer core 76 in contact with the inner surface of the clad 75, and an inner core 77 inside the outer core 76. The clad 75 has a tube shape in which the outer diameter and inner diameter are constant in the longitudinal direction and the thickness is uniform, like the clad 12 in FIG. The clad 75 is made of polyvinylidene fluoride (hereinafter referred to as PVDF) in the present embodiment, and is obtained by melt extrusion molding. However, the cladding 75 may be PMMA as in the previous embodiment, or may be another material as will be described in detail later. As with the clad 75, the outer core 76 has a tube shape in which the outer diameter and inner diameter are constant in the longitudinal direction and the thickness is uniform. The material of the outer core 76 is PMMA. In this embodiment, the clad 75 and the outer core 76 are integrally formed by melt extrusion at the same time. However, the present invention is not limited to this. For example, the clad 75 is obtained by melt extrusion molding, and a polymerizable compound such as MMA is injected into the clad 75, and a polymerization reaction is performed while rotating to form an outer core 76 made of PMMA or the like. A clad 75 and an outer core 76 may be formed.

  In FIG. 7, the horizontal axis indicates the cross-sectional radial direction of the preform 65, and the vertical axis indicates the refractive index. The refractive index means that the upper direction has a high value. The range indicated by the symbol (C) on the horizontal axis is the refractive index of the cladding 75 in FIG. 6, the range indicated by the symbol (D) is the refractive index of the outer core 76 in FIG. The range shown is the refractive index of the inner core 77 in FIG.

  As shown in FIG. 7, the inner core 77 has a refractive index that continuously increases from the boundary with the outer core 76 toward the center. The clad 75 has a lower refractive index than the outer core 76, and the outer core 77 has a lower refractive index than the inner core 77. In this embodiment, as shown in FIG. 7, the refractive index of the inner core 77 of the manufactured preform 65 is continuously increased from the outside of the circular cross-section toward the center. Furthermore, as a method for producing the inner core 77, an interfacial gel polymerization method is applied in the same manner as the method for producing the core 30 (see FIG. 2) of the above embodiment. That is, a polymerizable compound (hereinafter referred to as an inner core monomer) for generating an inner core is injected into the outer core 76, and the inner core monomer is polymerized to obtain the preform 65. In the radial direction of the circular cross section, the difference between the maximum value and the minimum value of the refractive index is preferably 0.001 or more and 0.3 or less. The monomer for the inner core of the present embodiment is MMA, and the outer core 76 and the inner core 77 after polymerization have a main component of PMMA. Therefore, although the boundary between the two is shown in FIG. 6 for convenience of explanation, the obtained preform 65 may not be clear as shown in FIG.

  In this embodiment, the material of the outer core 76 (hereinafter referred to as the outer core-forming polymer), that is, the glass transition point of PMMA here is Tg (° C.), the boiling point of the inner core monomer is Tb, When the temperature at the time of injecting the core monomer into the outer core 76 is TC (° C.), the inner core monomer is set so as to satisfy Tg−60 ≦ TC ≦ Tb or 40 ° C. or more and Tb or less. Adjust the temperature. Thus, the glass transition point of the material constituting the innermost layer of the tubular article into which the inner core monomer is injected is regarded as Tg in the above temperature range setting. The upper limit is more preferably Tb-10 (° C.) in terms of control. The more preferable range and the most preferable range of the adjustment temperature are the same as the temperature range depending on the temperature relationship between the core monomer and the clad forming polymer in the above embodiment. By satisfying this condition, when the inner core monomer is filled in the outer core 76, the temperature of the outer core 76 rises from the inner surface, and the higher the temperature after the rise, the more energy of the molecules of the outer core-forming polymer. This increases the affinity between the outer core-forming polymer and the filled core monomer molecules. The swelling layer in the initial polymerization stage of the inner core monomer has a uniform molecular density, and the inner surface of the outer core 76 and the orientation state of molecules in the vicinity thereof are made uniform. And cracks can be suppressed. Furthermore, the production method of the inner core 77 in this embodiment, for example, the temperature condition of the monomer to be injected into the tubular material, the decompression treatment of the tubular material, and the like are the same as the core production conditions of the above-described embodiment. By setting the manufacturing conditions by regarding the outer core 76 in the same manner as the cladding of the above embodiment, it is possible to suppress the occurrence of distortion, cracks, and bubbles.

  The present invention can also be applied to the production of a preform or POF having a larger layer structure. For example, in the second embodiment, the inner core can be formed in two layers. In the case where the present invention is applied to such a case, for example, the following method can be exemplified. First, as in the above embodiment, the inner core monomer is placed in the outer core, and rotational polymerization is performed to form the first inner core layer so that the center of the tube is hollow. That is, when the first inner core monomer is injected, when the glass transition point of the outer core polymer is Tg1 and the boiling point of the first inner core monomer is Tb1 (° C.), the temperature of the inner core monomer is The inner core monomer is heated in advance so that the temperature becomes Tg1-60 ° C. or higher and Tb1 or lower, or 40 ° C. or higher and Tb1 or lower. And about the tubular thing which consists of an outer core and a clad, it is preferable to give a pressure reduction process before injection | pouring. The polymerization of the first inner core monomer is preferably carried out under heating.

  The tubular product thus obtained has a first inner core layer, an outer core, and a clad, and then a second inner core layer is formed in the tubular product. The glass transition point of the material forming the first inner core is Tg2, and the boiling point of the second inner core monomer is Tb2 (° C.). Before injecting the monomer for forming the second inner core layer (second inner core monomer) into the obtained tubular product, the second inner core monomer is not less than (Tg2-60) and not more than Tb2. Heating is performed in advance so that the temperature becomes 40 ° C. or higher and Tb or lower. And like the time of producing | generating a 1st inner core, it is preferable to carry out pressure reduction processing of the tubular thing beforehand. Using this method, the refractive index in the radial direction of the preform can be continuously changed by selecting the material of each layer including the clad and outer core, the generation conditions including the polymerization conditions, etc. It can also be changed in stages. That is, a multi-step type preform or POF can be obtained.

  In the present invention, the clad and core materials constituting the preform are not particularly limited as long as the optical transmission function is not impaired. Particularly preferably, the organic material has high light transmittance. However, the material of the clad is a polymer having a refractive index lower than that of the core so that light transmitted through the core is totally reflected at the interface between the core and the clad. Further, an amorphous polymer is used so as not to cause optical anisotropy. Furthermore, it is more preferable that the core and the clad are polymers having excellent adhesion to each other, and these are excellent in mechanical properties indicated by toughness and the like and excellent in heat and moisture resistance.

  Examples include (meth) acrylic acid esters (fluorine-free (meth) acrylic acid ester (a), fluorine-containing (meth) acrylic acid ester (b)), styrenic compound (c), vinyl esters (d ), And bisphenol A, which is a raw material of polycarbonates, can be polymerized using a polymerizable compound. As the clad forming polymer, polyvinylidene fluoride (PVDF) is also preferable. Examples include homopolymers obtained by polymerizing each of these as raw materials, copolymers obtained by combining two or more of these, and mixtures of various combinations of the above homopolymers and copolymers. it can. In the case of using a mixture, the boiling point Tb is defined as the lowest temperature among the boiling points of a plurality of raw material compounds constituting the mixture, or the temperature after the boiling point is lowered when the boiling point is lowered by forming an azeotropic mixture. . In the case of a copolymer and a blend polymer obtained using a mixture as a raw material, the glass transition point of each copolymer or blend polymer is defined as Tg. And among these, what contains (meth) acrylic acid esters or a fluorine-containing polymer as a component is more preferable when comprising an optical transmission body. Next, the above example will be described in more detail.

Examples of (a) fluorine-free methacrylic acid ester and fluorine-free acrylic acid ester include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, tert-butyl methacrylate, benzyl methacrylate, phenyl methacrylate, and methacrylic acid. Examples include cyclohexyl, diphenylmethyl methacrylate, tricyclo [5 · 2 · 1 · 0 ^2,6 ] decanyl methacrylate, adamantyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, methyl acrylate, ethyl acrylate, acrylic acid -Tert-butyl, phenyl acrylate and the like.

  In addition, (b) fluorine-containing acrylic acid ester and fluorine-containing methacrylate ester include 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3 , 3-pentafluoropropyl methacrylate, 1-trifluoromethyl-2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2, Examples include 3,3,4,4-hexafluorobutyl methacrylate.

  Furthermore, (c) styrene compounds include styrene, α-methylstyrene, chlorostyrene, bromostyrene, and the like. Furthermore, (d) vinyl esters include vinyl acetate, vinyl benzoate, vinyl phenyl acetate, vinyl chloroacetate and the like. Of course, the present invention is not limited to these, and the refractive index of a polymer composed of a polymerizable compound alone or a copolymer may have a predetermined refractive index distribution in the molded body when molded into an optical transmission body. In addition, it is preferable to determine the type and composition ratio.

  Moreover, as a preferable polymer for forming the cladding, the following can be exemplified in addition to the above-mentioned various compounds. For example, a copolymer of methyl methacrylate (MMA) and a fluorinated (meth) acrylate such as trifluoroethyl methacrylate (FMA) or hexafluoroisopropyl methacrylate can be given. In addition, a copolymer of MMA and an alicyclic (meth) acrylate such as (meth) acrylate having a branch such as tert-butyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, tricyclodecanyl methacrylate, etc. is there. Furthermore, polycarbonate (PC), norbornene-based resin (for example, ZEONEX (registered trademark: manufactured by Nippon Zeon Co., Ltd.)), functional norbornene-based resin (for example, ARTON (registered trademark: manufactured by JSR)), fluorine resin (for example, Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.) can also be used. In addition, a fluororesin copolymer (for example, PVDF copolymer), tetrafluoroethylene perfluoro (alkyl vinyl ether (PFA) random copolymer, chlorotrifluoroethylene (CTFE) copolymer, or the like may be used. In addition, the hydrogen atom (H) of these polymers can be replaced with a deuterium atom (D) to reduce transmission loss.

  Furthermore, when an optical member is used for near-infrared light, absorption loss due to the C—H bond to be formed occurs, so that it is described in Japanese Patent No. 3332922 and Japanese Patent Application Laid-Open No. 2003-192708. In addition, by using a polymer in which the hydrogen atom of C—H bond is substituted with deuterium atom or fluorine, the wavelength region causing this transmission loss can be lengthened, and the loss of transmission signal light can be reduced. Can do. Examples of such polymers include deuterated polymethyl methacrylate (PMMA-d8), polytrifluoroethyl methacrylate (P3FMA), polyhexafluoroisopropyl 2-fluoroacrylate (HFIP 2-FA), and the like. it can. In addition, in order not to impair the transparency after polymerization of the compound as a raw material, it is desirable that impurities and foreign substances serving as scattering sources are sufficiently removed before polymerization.

  In the case of polymerizing the polymer, a polymerization initiator may be used. As the polymerization initiator, for example, there are various types that generate radicals. For example, benzoyl peroxide (BPO), tert-butylperoxy-2-ethylhexanate (PBO), di-tert-butyl peroxide (PBD), tert-butylperoxyisopropyl carbonate (PBI) ) And peroxide compounds such as n-butyl-4,4-bis (tert-butylperoxy) valerate (PHV). 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (2-methylpropane), 2,2′-azobis (2-methylbutane), 2,2′-azobis (2-methylpentane), 2,2′-azobis (2,3-dimethylbutane), 2,2 '-Azobis (2-methylhexane), 2,2'-azobis (2,4-dimethylpentane), 2,2'-azobis (2,3,3-trimethylbutane), 2,2'-azobis (2 , 4,4-trimethylpentane), 3,3′-azobis (3-methylpentane), 3,3′-azobis (3-methylhexane), 3,3′-azobis (3,4-dimethylpentane), 3,3'-azobis 3-ethylpentane), dimethyl-2,2′-azobis (2-methylpropionate), diethyl-2,2′-azobis (2-methylpropionate), di-tert-butyl-2,2 ′ -Azo compounds such as azobis (2-methylpropionate). In addition, a polymerization initiator is not limited to these, Moreover, you may use 2 or more types together.

  In order to keep various physical property values such as mechanical properties and thermophysical properties uniform when used as a polymer, it is preferable to adjust the degree of polymerization. A chain transfer agent can be used to adjust the degree of polymerization. About a chain transfer agent, according to the kind of polymerizable monomer used together, a kind and addition amount can be selected suitably. The chain transfer constant of the chain transfer agent for each monomer can be referred to, for example, Polymer Handbook 3rd edition (edited by J. BRANDRUP and EH IMMERGUT, published by JOHN WILEY & SON). The chain transfer constant can also be obtained by experiment with reference to Takayuki Otsu and Masaaki Kinoshita "Experimental Method for Polymer Synthesis", Kagaku Dojin, published in 1972.

  Examples of chain transfer agents include alkyl mercaptans (eg, n-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, tert-dodecyl mercaptan, etc.), thiophenols (thiophenol, m-bromothio). Phenol, p-bromothiophenol, m-toluenethiol, p-toluenethiol, etc.) are preferably used. In particular, it is preferable to use an alkyl mercaptan such as n-octyl mercaptan, n-lauryl mercaptan, and tert-dodecyl mercaptan. A chain transfer agent in which a hydrogen atom of a C—H bond is substituted with a deuterium atom or a fluorine atom can also be used. Of course, the chain transfer agent is not limited to these, and two or more of these chain transfer agents may be used in combination.

  When the core part, which is the center part of the POF, is a GI-type POF having a refractive index that varies from the center toward the outer periphery, the transmission performance is improved, so that optical communication over a wider band can be performed. It can use preferably for a use. As a method for imparting a refractive index distribution, a polymer that forms a core part is incorporated with a plurality of polymer units, a copolymer that is a combination of these polymers, or a refractive index distribution in a polymer matrix. It is necessary to add an additive for imparting (hereinafter referred to as a dopant).

The dopant is a compound having a refractive index different from that of the polymerizable compound as described above. The refractive index difference is preferably 0.005 or more. The dopant has the property that the polymer containing it has a higher refractive index than the additive-free polymer. These have a difference in solubility parameter of 7 (cal / cm ³ ) in comparison with a polymer produced by monomer synthesis as described in Japanese Patent No. 3332922 and JP-A-5-173026. ^{In addition to being} within ^1/2 , the difference in refractive index is 0.001 or more, and the polymer containing this has the property of changing the refractive index as compared with the additive-free polymer. Any of those which can coexist and are stable under the polymerization conditions (polymerization conditions such as heating and pressurization) of the polymerizable monomer which is the above-mentioned raw material can be used.

  The dopant may be a polymerizable compound. When a dopant of a polymerizable compound is used, it is preferable to use a copolymer that has a property of increasing the refractive index compared to a polymer that does not include the copolymer as a copolymer component. It has the above properties, can stably coexist with the polymer, and is stable under various polymerization conditions (polymerization conditions such as heating and pressurization) of the polymerizable compound that is the core monomer or the cladding material described above. Can be used as a dopant. In this embodiment, the core monomer contains a dopant, and in the step of forming the core part, the progress direction of the polymerization is controlled by the interfacial gel polymerization method, the concentration of the refractive index adjusting agent is given a gradient, Although a method of forming a refractive index distribution structure based on the concentration distribution of the refractive index adjusting agent is illustrated, there is also known a method of diffusing the refractive index adjusting agent after forming a preform (hereinafter referred to as refractive index). (A core portion having a distribution of 2 is referred to as a “refractive index distribution type core portion”). By forming the gradient index core portion, the obtained optical member becomes a gradient index plastic optical member having a wide transmission band.

  Examples of the dopant include benzyl benzoate (BEN), diphenyl sulfide (DPS), triphenyl phosphate (TPP), benzyl-n-butyl phthalate (BBP), diphenyl phthalate (DPP), and biphenyl (DP). , Diphenylmethane (DPM), tricresyl phosphate (TCP), diphenyl sulfoxide (DPSO) and the like, among which BEN, DPS, TPP and DPSO are preferable. The dopant may be a polymerizable compound such as tribromophenyl methacrylate. In that case, when forming the matrix, the polymerizable monomer and the polymerizable dopant are copolymerized, so that various properties (especially optical properties). ) Is more difficult to control, but may be advantageous in terms of heat resistance. By adjusting the concentration and distribution of the dopant in the core, the refractive index of the plastic optical fiber can be changed to a desired value.

  About each addition amount of the polymerization initiator mentioned above, a chain transfer agent, and a refractive index regulator, a preferable range can be suitably determined according to the kind etc. of the monomer for cores to be used. In this embodiment, the polymerization initiator is added so that it may become 0.005-0.050 mass% with respect to the monomer for cores, and this addition rate is 0.010-0.020 mass%. More preferably. The chain transfer agent is added to the core monomer so as to be 0.10 to 0.40% by mass, and the addition rate may be 0.15 to 0.30% by mass. More preferred. And like this embodiment, it is preferable that the addition rate in the case of adding a dopant shall be 1 mass% or more and 50 mass% or less with respect to the monomer for cores.

  In addition, other additives can be added to the core part, the clad part, or a part thereof within a range that does not deteriorate the optical transmission performance. For example, a stabilizer can be added to the core portion or a part thereof for the purpose of improving weather resistance, durability, and the like. Further, for the purpose of improving optical transmission performance, a stimulated emission functional compound for optical signal amplification can be added. By adding the compound, the attenuated signal light can be amplified by the pumping light, and the transmission distance is improved. For example, it can be used as a fiber amplifier in a part of the optical transmission link. These additives can also be contained in the core part, the clad part or a part of them by adding to the various polymerizable compounds as the raw material and then polymerizing.

  As described in Japanese Patent No. 3332922, a method for manufacturing a GI POF preform is to create a resin hollow tube as a cladding, and inject a resin composition forming a core into the tube, A method of forming the core part by polymerizing a polymer by an interfacial gel polymerization method which is a kind of polymerization method can be exemplified. The polymerization conditions in this case, that is, the polymerization temperature and the ordering time vary depending on the monomers used and the polymerization initiator, but there are generally preferred conditions. With respect to the conditions, for example, the polymerization temperature is preferably 60 ° C. or higher and preferably not higher than the glass transition point of the polymer to be produced, and preferably 60 ° C. or higher and 150 ° C. or lower. For example, the polymerization time is preferably 5 to 72 hours, and more preferably 5 to 48 hours. The polymerization reaction is preferably performed in an inert gas atmosphere, and pressurization or decompression may be performed as necessary. In addition, by applying the polymerization conditions described in International Publication No. 03/19252 pamphlet, a core portion free from density fluctuation can be formed. In addition, a method for forming a core part in which polymerizable compositions having different refractive indexes after polymerization are sequentially added is also known. In addition, the manufacturing method of the preform of the GI optical fiber used in the present invention is not limited to the interfacial gel polymerization method as described above. As described above, as the resin composition, a resin composition having a single refractive index to which a refractive index adjusting agent is added, a resin having a different refractive index, a copolymer, or the like is used. In addition to the GI type, plastic optical fibers having various refractive index profiles such as a single mode type and a step index type are known, and the present invention can also be applied to these POF manufacturing methods.

  In the case of POF, by bending, improving weather resistance, suppressing performance degradation due to moisture absorption, improving tensile strength, imparting stepping resistance, imparting flame resistance, protecting against chemical damage, preventing noise from external light, coloring, etc. For the purpose of improving commercial value, usually, the surface is coated with one or more protective layers.

  Specific examples of the protective layer forming material include the following materials. Since these have high elasticity, they are also effective in terms of imparting mechanical properties such as bending. First, rubber which is one form of polymer can be used. Specifically, isoprene rubber (for example, natural rubber, isoprene rubber, etc.), butadiene rubber (for example, styrene-butadiene copolymer rubber, butadiene rubber, etc.), diene special rubber (for example, nitrile rubber, chloroprene rubber, etc.) ), Olefin rubber (for example, ethylene-propylene rubber, acrylic rubber, butyl rubber, halogenated butyl rubber, etc.), ether rubber, polysulfide rubber, urethane rubber and the like.

  Further, as the protective layer forming material, it is possible to use a liquid rubber that exhibits fluidity at room temperature and is cured by heating to lose its fluidity. Specifically, polydiene-based (for example, basic structure is polyisoprene, polybutadiene, butadiene-acrylonitrile copolymer, polychloroprene, etc.), polyolefin-based (for example, basic structure is polyolefin, polyisobutylene, etc.), polyether-based (for example, , Basic structure is poly (oxypropylene), etc., polysulfide type (eg, basic structure is poly (oxyalkylene disulfide), etc.), polysiloxane type (eg, basic structure is poly (dimethylsiloxane), etc.) Can do.

  A thermoplastic elastomer (TPE) can also be used as the protective layer forming material. Thermoplastic elastomers are a group of substances that exhibit rubber elasticity at room temperature and are plasticized at high temperatures and are easy to mold. Specific examples include styrene TPE, olefin TPE, vinyl chloride TPE, urethane TPE, ester TPE, amide TPE, and the like. The listed polymers are not particularly limited to the above materials as long as they can be molded at a glass transition temperature Tg or lower of the strand polymer. Copolymers or mixed polymers other than the above materials or other than the above are used. You can also

  Moreover, what hardens the liquid which mixed the polymer precursor, the reactive agent, etc. can be used as a protective layer forming material. Examples thereof include a one-component thermosetting urethane composition produced from an NCO block prepolymer and a fine powder coating amine described in JP-A-10-158353. Further, a one-component thermosetting urethane composition comprising an NCO group-containing urethane prepolymer described in International Publication No. 95/26374 pamphlet and a solid amine of 20 μm or less can also be used. In addition, additives such as flame retardants, antioxidants, radical scavengers, lubricants, and various fillers composed of inorganic compounds and / or organic compounds can be added for the purpose of improving performance.

  In the optical transmission body of the present invention, if necessary, the protective layer may be a primary coating layer, and a secondary (or multilayer) coating layer may be further provided on the outer periphery. When the primary coating has a sufficient thickness, thermal damage is reduced due to the presence of the primary coating, so the limit of the curing temperature of the material of the secondary coating layer is the case where the primary coating layer is coated. Compared to, it can be loosened. As described above, a flame retardant, an ultraviolet absorber, an antioxidant, a radical scavenger, a light raising agent, a lubricant and the like may be introduced into the secondary coating layer. Some flame retardants include halogen-containing resins such as bromine, additives and phosphorus, but metal hydroxides can be preferably used as flame retardants from the viewpoint of safety such as reduction of toxic gases. . Since the metal hydroxide has water as crystal water in the inside thereof, and the attached water cannot be completely removed during the production process, the flame retardant coating with the metal hydroxide is the primary coating layer of the present invention. It is desirable to provide a moisture-resistant coating on the outer layer and further provide a coating layer on the outer layer.

  Moreover, in order to provide a plurality of functions, coatings having various functions may be laminated. For example, in addition to the above-mentioned flame retardancy, it is possible to have a barrier layer for suppressing moisture absorption or a moisture absorbing material for removing moisture, such as a moisture absorbing tape or moisture absorbing gel, in the coating layer or between the coating layers, and flexible. A cushioning material such as a flexible material layer or a foamed layer for stress relaxation at times, a reinforcing layer for improving rigidity, and the like can be selected and provided depending on the application. In addition to the resin, if the thermoplastic resin contains a fiber having a high elastic modulus (so-called tensile fiber) and / or a highly rigid metal wire, the mechanical strength of the resulting cable can be reinforced. It is preferable because it is possible. Examples of the tensile strength fiber include aramid fiber, polyester fiber, and polyamide fiber. Examples of the metal wire include stainless steel wire, zinc alloy wire, copper wire and the like. None of these are limited to those described above. In addition, a metal tube exterior for protection, an aerial support line, and a mechanism for improving workability during wiring can be incorporated.

  In addition, depending on the type of use, the cable shape is a collective cable in which the strands are concentrically arranged, an aspect called a tape core wire arranged in a row, and a collective cable in which they are gathered together with a presser roll or wrap sheath The form can be selected according to the situation.

  Moreover, it is preferable that the optical device using the POF obtained according to the present invention is securely fixed at the end portion by using an optical connector for connection. As the connector, it is possible to use various commercially available connectors such as PN type, SMA type, SMI type, F05 type, MU type, FC type, and SC type that are generally known.

  The optical transmission body of the present invention is combined with various light emitting elements, light receiving elements, optical switches, optical isolators, optical integrated circuits, optical signal processing apparatuses including optical components such as optical transceiver modules, and the like. Moreover, you may combine with another optical fiber etc. as needed. Any known technique can be applied as a technique related to them. For example, the basic and actual of plastic optical fiber (published by NTS Corporation), Nikkei Electronics 2001.1.2.3, pages 110 to 127, “Printed Wiring You can refer to "This time, optical components are mounted on the board." Combined with various technologies described in the above documents, internal wiring in computers and various digital devices, internal wiring in vehicles and ships, optical terminals and digital devices, optical links between digital devices, general households and housing complexes・ Suitable for optical transmission systems suitable for short distances such as high-speed, large-capacity data communications and control applications that are not affected by electromagnetic waves, including optical LANs in factories, offices, hospitals, schools, etc. Can be used.

  Further, IEICE TRANS. ELECTRON. , VOL. E84-C, No. 3, MARCH 2001, p. 339-344 “High-Uniformity Star Coupler Using Diffused Light Transmission”, Journal of Japan Institute of Electronics Packaging, Vol. 3, No. 6,2000, pages 476 to 480, which are described in “Interconnection by Optical Sheet Bus Technology”, and the arrangement of light emitting elements on the waveguide surface described in Japanese Patent Application Laid-Open No. 2003-152284; , JP-A-2002-90571, JP-A-2001-290055, and the like; JP-A-2001-74971, JP-A-2000-329962, JP-A-2001-74966, JP-A-2001-74968 , JP 2001-318263, JP 2001-31840, etc .; optical branch couplers described in JP 2000-241655 A; optical star couplers described in JP 2000-241655, etc .; Optical signal transmission devices described in Japanese Patent Laid-Open Nos. 2002-101044 and 2001-305395 An optical data bus system; an optical signal processing apparatus described in JP-A No. 2002-23011; an optical signal cross-connect system described in JP-A No. 2001-86537; an optical transmission system described in JP-A No. 2002-26815; Multi-function systems described in JP 2001-339554 A, JP 2001-339555 A, etc .; and various optical waveguides, optical splitters, optical couplers, optical multiplexers, optical demultiplexers, etc. Thus, a more advanced optical transmission system using multiplexed transmission / reception can be constructed. In addition to the above light transmission applications, it can also be used in the fields of illumination (light guide), energy transmission, illumination, and sensors.

  In addition, this invention is not limited to manufacture of GI type | mold POF as demonstrated in said embodiment. That is, application is not limited only to the interfacial gel polymerization method as described above. For example, the present invention can be applied to the manufacture of a step index (SI) type or single mode (SM) type POF and its preform. And this invention is not limited to the optical transmission body formed with a tubular clad and the core in the clad, It can apply also to a flat optical transmission body, a lens, etc. For example, in the case of a plate-shaped optical transmission body such as an optical waveguide, the present invention is applied when the refractive index is manufactured so as to be different in the thickness direction of at least a part of the plate (sometimes referred to as axial GRIN). Can be applied. In the case of a spherical product, the present invention can be applied to a case where the refractive index is different from the center of the sphere in the radial direction to the outer surface (sometimes referred to as “spherical GRIN”).

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated concretely, this invention is not limited to this. In the following Examples, Example 3 and Example 4 were performed as comparative examples for Example 1 and Example 2.

  The clad 12 was manufactured using a sufficiently rigid polymerization vessel having an inner diameter corresponding to the outer diameter of the target preform 15. This polymerization container is a cylindrical container having an inner diameter of 22 mm and a length of 600 mm. A predetermined amount of methyl methacrylate (MMA) from which moisture was removed to 100 ppm or less was injected into this polymerization vessel. Dimethylazobisisobutyrate was used as the polymerization initiator for MMA, and n-dodecyl mercaptan was used as the chain transfer agent (molecular weight modifier). Dimethylazobisisobutyrate was mixed with 0.05% by mass and n-dodecyl mercaptan was mixed with 0.4% by mass with respect to MMA.

  Thereafter, the polymerization vessel into which the MMA solution was injected was subjected to ultrasonic deaeration for 5 minutes under reduced pressure, and then the polymerization vessel was sealed. The polymerization vessel was placed in a 70 ° C. hot water bath and preliminarily polymerized for 2 hours while shaking was applied. Thereafter, the polymerization vessel was placed in a horizontal state at 65 ° C. and held in a state where the height direction was horizontal. The polymerization vessel was rotated at 3000 rpm and polymerized under heating for 1 hour, then heated to 70 ° C., and further polymerized under heating for 4 hours. Thereafter, heat treatment was performed at 90 ° C. for 24 hours to obtain a cylindrical tube made of PMMA, which was used as the cladding 12. In addition, Tg of obtained PMMA was 105 degreeC.

Next, the obtained clad 12 was taken out from the polymerization vessel and held for 2 hours under a reduced pressure of 4 × 10 ² Pa. Thereafter, MMA as a core monomer and a dopant were injected into the clad 12. MMA is a solution in which moisture is removed to 100 ppm or less. Diphenyl sulfide is used as a dopant, and 7% by mass is mixed with MMA. The boiling point of MMA is 100 ° C. Prior to this injection, the mixed solution was heated to 70 ° C., which is 35 ° C. lower than the Tg of PMMA in the cladding 12. Then, the filtrate was directly injected into the clad 12 while being filtered through a membrane filter made of ethylene tetrafluoride having an accuracy of 0.2 μm. At this time, no crack was generated on the inner surface of the clad 12.

  Di-t-butyl peroxide (10-hour half-life temperature is 123.7 ° C.) was used as the polymerization initiator, and dodecyl mercaptan was used as the chain transfer agent. Di-t-butyl peroxide was blended in 0.016% by mass and dodecyl mercaptan in 0.27% by weight with respect to MMA. The clad 12 into which MMA or the like was injected was subjected to ultrasonic deaeration for 5 minutes under reduced pressure, then inserted into the glass tube 52 and set in the polymerization vessel 41. The glass tube 52 has an inner diameter that is 9% wider than the outer diameter of the cladding 12. The glass tube 52 was allowed to stand vertically in the polymerization vessel 51. Thereafter, the inside of the polymerization vessel 41 was replaced with nitrogen, and then pressurized to 0.05 Mpa and polymerized by heating at 100 ° C. for 48 hours. Thereafter, heat polymerization and heat treatment were performed at 120 ° C. for 24 hours. After the polymerization was completed, the preform 15 was obtained after the temperature was lowered to 80 ° C., which is equal to or lower than the Tg of the PMMA of the core 30, at a cooling rate of 0.01 ° C./min while maintaining the pressurization amount at 0.05 Mpa.

  The resulting preform 15 did not contain bubbles due to volume shrinkage when the polymerization was completed. This preform 15 was heated and stretched at 230 ° C. to produce POF 17 having a diameter of about 400 to 500 μm. In the stretching step 16, no bubbles were observed in the preform 15, and 500m POF 17 could be stably obtained. When the transmission loss value of the obtained POF 17 was measured, it was 170 dB / km at a wavelength of 650 nm. Further, when the transmission band of the obtained POF 100 m was measured, it was 1.5 GHz. Further, when the preform obtained by the same method was stretched to have a core diameter of 300 μm ± 15 μm, there was no foaming at the time of stretching, and a product exhibiting almost the same transmission performance was obtained. Furthermore, when the preform obtained by the same method was stretched so that the outer diameter was 300 μm ± 15 μm, there was no foaming at the time of stretching, and the transmission performance was almost the same.

  A hollow tube made of polyvinylidene fluoride (PVDF) having an outer diameter of 20 mm, an inner diameter of 19 mm, and a length of 60 cm prepared by extrusion molding was set as a clad 75 in the polymerization container. The clad 75 is made by melt extrusion molding. The polymerization vessel has a sufficiently rigid inner diameter of 20 mm and a length of 60 cm. The clad 75 is injected with a predetermined amount of the MMA solution used in the clad fabrication of Example 1 and polymerized under heating while rotating to form a layer made of PMMA on the inner surface of the clad 75. Was used as the outer core 76. Thus, the first member composed of the outer core and the clad contains a fluorine-based polymer, and the inner surface thereof is an amorphous polymer PMMA.

Thereafter, the clad 75 having the outer core 76 was held at 4 × 10 ² Pa for 2 hours. Then, MMA heated up to 70 ° C., which is 30 ° C. lower than the boiling point Tb at normal pressure of MMA, was injected and polymerized under heating and pressurization to form a polymerized portion as an inner core 77 to obtain a preform 65. In the step of injecting the MMA for generating the inner core 77 into the outer core 76, no crack was generated, and no bubbles were mixed in the obtained preform 65. In the stretching process, no bubbles were observed in the preform 65, and 300 m of POF having an outer diameter of 400 to 500 μm could be stably obtained. When the transmission loss value of the obtained POF was measured, it was 170 dB / km at a wavelength of 650 nm. Further, when the transmission band of the obtained fiber 100 m was measured, it was 1.0 GHz. Further, when the preform obtained by the same method was stretched to have a core diameter of 300 μm ± 15 μm, there was no foaming at the time of stretching, and a product exhibiting almost the same transmission performance was obtained. Furthermore, when the preform obtained by the same method was stretched so that the outer diameter was 300 μm ± 15 μm, there was no foaming at the time of stretching, and the transmission performance was almost the same.

  In the clad 12 produced by the method of Example 1, the temperature is raised to 30 ° C., which is 75 ° C. lower than the Tg of PMMA on which the clad 12 is formed and 70 ° C. lower than the boiling point (100 ° C.) at normal pressure of MMA. The MMA mixed solution was injected. At the time of injection, a large number of cracks occurred on the inner surface of the clad 12. Thereafter, the core 30 was polymerized under heating and pressure in the same manner as in Example 1 to obtain a preform 15. In the obtained preform 15, bubbles were mixed, and a large number of bubbles were generated in the stretching process of the preform 15. The transmission loss of the obtained POF was 250 dB / km in the 650 nm wavelength band.

  Although the core monomer MMA solution placed in the clad 12 produced by the method of Example 1 was heated to 110 ° C., which is 10 ° C. higher than the boiling point Tb at normal pressure, and injection into the hollow portion was attempted. The MMA solution boiled and injection into the hollow tube was not possible.

It is the schematic which shows the manufacturing process of the plastic optical fiber as embodiment of this invention. It is sectional drawing of the preform which is embodiment of this invention. It is a figure which shows the refractive index in the radial direction of a preform. It is sectional drawing which shows the superposition | polymerization apparatus for producing | generating a core part. It is the schematic which shows the manufacturing process of the plastic optical fiber as another embodiment. It is sectional drawing of the preform which is another embodiment of this invention. It is a figure which shows the refractive index in the radial direction of the preform in FIG.

Explanation of symbols

12 Cladding 15 Preform 30 Core 40 Polymerizer 41 Polymerization Container 41a Container Body 41b Lid 44 Pressure Gauge 45 Pressure Controller 47 Thermometer 48 Temperature Controller 51 Nitrogen Supply Source 65 Preform 75 Cladding 76 Outer Core 77 Inner Core V1 Valve

Claims (13)

An optical transmission body using an injection step of injecting a polymerizable compound into a first member formed in a tubular shape with a material containing a polymer, and a polymerization step of generating a second member by polymerizing the polymerizable compound In the method of manufacturing
The temperature of the polymerizable compound in the injection step is TC (° C.),
The glass transition point of the polymer of the first member is Tg (° C.),
When the boiling point of the polymerizable compound is Tb,
Tg-60 ≦ TC ≦ Tb or 40 ≦ TC ≦ Tb
An optical transmission body manufacturing method characterized by satisfying:   2. The method of manufacturing an optical transmission body according to claim 1, wherein the inner surface of the first member is subjected to reduced pressure for a predetermined time before the injecting step.   The method for producing an optical transmission body according to claim 1, wherein the polymerizable compound is polymerized under heating.   The method for producing an optical transmission body according to any one of claims 1 to 3, wherein the polymerizable compound is polymerized under pressure.   5. The method of manufacturing an optical transmission body according to claim 1, wherein the first member has a layer generated by a rotational polymerization method. 6.   6. The method of manufacturing an optical transmission body according to claim 1, wherein the first member has a layer formed by a melt extrusion method.   The method for manufacturing an optical transmission body according to claim 1, wherein the second member has a higher refractive index than that of the first member.   The refractive index of the first member or the second member decreases continuously or stepwise from the radial center to the outer periphery of the circular section, and the difference between the maximum value and the minimum value of the refractive index is reduced. It is 0.001 or more and 0.3 or less, The manufacturing method of the optical transmission body as described in any one of Claim 1 thru | or 7 characterized by the above-mentioned.   The method for manufacturing an optical transmission body according to claim 1, wherein the first member includes a fluorine-containing polymer.   The method for manufacturing an optical transmission body according to claim 1, wherein at least an inner surface of the first member includes an amorphous polymer. The optical transmission body manufactured by the manufacturing method according to any one of claims 1 to 10 is melt-drawn into an optical fiber,
At least a part of the first member becomes a clad portion of the optical fiber,
The method for manufacturing an optical fiber, wherein the second member serves as a core portion of the optical fiber.   An optical transmission body manufactured by the manufacturing method according to claim 1.   An optical fiber manufactured by the manufacturing method according to claim 11.

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